Conventionally, a lubricant supply unit (lubricating device) which supplies a very small amount of lubricant to a rolling bearing has been proposed (see Japanese Patent Publication (Kokai) No. 2002-130593). In the lubricant supply unit, a tank is disposed distantly from a position where the rolling bearing is disposed, a nozzle is disposed so as to face a space between an inner ring and an outer ring of the rolling bearing, and the tank and the nozzle are connected together via a lubricant supply path.
The prior art lubricant supply unit is required to be disposed as a unit separate from the rolling bearing, and hence its installation is troublesome. By contrast, a configuration in which a lubrication pump for discharging lubricant is disposed inside a rolling bearing (see Japanese Patent Publication (Kokai) No. HEI3-113119).
As a bearing device in which lubricant is automatically supplied to a rolling bearing, a bearing device which is to be used in a spindle of a machine tool is known. As shown in FIG. 10, an example of such a bearing device is configured by: a lubricant storage chamber 23 which temporarily stores lubricant supplied from a lubricant tank 21 to a rolling bearing 20 by a pump 22; a diaphragm 24 which is disposed in the lubricant storage chamber 23; a nozzle 25 which is formed in a portion excluding the diaphragm 24; and a piezoelectric element 26 which applies vibrations to the diaphragm 24 so as to fluctuate the pressure of the lubricant storage chamber 23. According to the configuration, the lubricant is supplied to a rolling element 27 and raceway surfaces 20a, 20b of inner and outer rings of the rolling bearing 20 via the nozzle 25 (see Japanese Patent Publication (Kokai) No. 2002-213687).
Alternatively, as a bearing device which is similarly to be used similarly in a machine tool, a bearing device configured so that a larger amount of lubricant is supplied when the temperature of a bearing is raised has been proposed. As shown in FIG. 11(A), the bearing device comprises: a spacer 34 which is fitted onto a rotating shaft 31 adjacently to a bearing inner ring 32 fitted onto the rotating shaft 31; and a lubricant supplying mechanism 30 which supplies lubricant G into a space Q between an outer ring 33 and the inner ring 32. The lubricant supplying mechanism has: a lubricant chamber 36 disposed in the spacer 34; a lubricant flow path 35 through which the lubricant G is supplied from the lubricant chamber 36 to the space Q; a lubricant discharging hole 37; and a lubricant supplying groove 38. The lubricant chamber 36 comprises a lubricant chamber internal pressure adjusting mechanism 39 which is communicatable with or not communicatable with the atmosphere.
The lubricant chamber internal pressure adjusting mechanism 39 is configured by: an atmosphere introducing hole 42 which communicates with the lubricant chamber 36 via an atmosphere introducing groove 40 to equalize the internal pressure of the lubricant chamber 36 with the atmospheric pressure; and a tab 41 which is made of a shape-memory alloy, and which normally closes the atmosphere introducing hole 42 so as to hermetically seal the lubricant chamber 36, and which, when the temperature is raised, deforms so as to cause the atmosphere introducing hole 42 to communicate with the atmosphere (see Japanese Patent Publication (Kokai) No. 2002-250352). FIG. 11(B) is an enlarged view taken along the line M-M in FIG. 11(A), looking in the direction of the arrows.
In the prior art example disclosed in Japanese Patent Publication (Kokai) No. HEI3-113119, the lubricant pump is a vane pump, and has a large external size. Therefore, the size of the rolling bearing is inevitably made larger, and it is necessary to ensure a pump mounting area in the outer ring of the rolling bearing. Accordingly, there is a fear that the cost is increased. In addition, a tank for storing the lubricant must be disposed outside the rolling bearing.
In a conventionally proposed bearing device in which lubricant is supplied, a lubricant supplying device is disposed externally, and a spacer is disposed on the side of the inner ring in addition to the inner ring, so that the required space is large as a whole. Therefore, downsizing thereof is limited. In order to solve such problems, the assignee of the present invention has proposed a rolling bearing device in which lubricant is supplied to rolling elements, or raceway surfaces of a stationary race ring and a rotating race ring on the side of the stationary race ring of the rolling bearing (see Japanese Patent Application No. 2002-267838).
In the rolling bearing device, a lubricant supply unit which supplies lubricant as necessary to the rolling elements, or the raceway surfaces of the stationary and rotating race rings is additionally disposed on the side of the stationary race ring of the rolling bearing. The lubricant supply unit comprises: a tank which stores lubricant; a micro pump which sucks and discharges the lubricant in the tank; and a driving portion (electric generator) which drives the micro pump. In the configuration, however, a magnet and a coil for the generator must be mounted, and hence there are severe restrictions on the space. Thus, it is difficult for the current configuration to be applied to a bearing of a smaller size. In addition, in order to make it possible to be applied to a bearing of a smaller size, it is necessary to provide a bearing device in which the size of the unit is further reduced, and the supply amount of lubricant can be adjusted so as to automatically supply the lubricant for a long term.
The invention has been conducted in order to solve the above-discussed problems. It is an object of the invention to provide a bearing device in which a lubricant supply unit to be attached to a bearing is compact and slim, so that it can be mounted on a bearing of a smaller size and lubricant can be automatically supplied for a long term.